Heleen skates with a dog on Olkhon Island on Lake Baikal in Siberia, Russia. .They are a group of five people: Justin Jin (Chinese-British), Heleen van Geest (Dutch), Nastya and Misha Martynov (Russian) and their Russian guide Arkady. .They pulled their sledges 80 km across the world's deepest lake, taking a break on Olkhon, the world's forth-largest lake-bound island. They slept two nights on the ice in -15c. .Baikal, the world's largest lake by volume, contains one-fifth of the earth's fresh water and plunges to a depth of 1,637 metres..The lake is frozen from November to April, allowing people to cross by cars and lorries.